This application is based on Japanese patent applications No. HEI 11-076802 and No. HEI-11-076804, both filed on Mar. 19, 1999, all the contents of which are incorporated herein by reference.
a) Field of the Invention
The present invention relates to a liquid crystal display apparatus and an electronic instrument using the same, and more particularly to an active matrix type liquid crystal display apparatus having semiconductor active elements such as thin film transistors (hereinafter abbreviated as xe2x80x9cTFTxe2x80x9d) as a switching element of each pixel, and to an electronic instrument using such a liquid crystal display apparatus.
b) Description of the Related Art
In an active matrix liquid crystal display apparatus, a plurality of scan lines are disposed in a row direction and a plurality of signal lines are disposed in a column direction. A pixel is disposed at each cross point of the matrix pattern of the scan and signal lines. Each pixel includes a pixel electrode and a switching element connected to the pixel electrode. Pixel image data of the active matrix liquid crystal display is controlled to be turned on and off by the switching element. Display medium of the apparatus is liquid crystal.
MIM (metal insulator metal) elements or three-electrode elements, particularly TFT having a gate, source and drain, are used as the switching elements. In this specification, a current terminal connected to a pixel electrode is called a drain, and the other current terminal connected to a signal line is called a source. A unit cell including a pixel electrode and a TFT is called a pixel. An image is displayed in a pixel area unit where a number of pixels are disposed in a matrix pattern.
A scan line (gate line) of each row disposed in a row direction is connected to the gate electrodes of TFTs of that row. A signal line (source line) of each column disposed in a column direction is connected to the sources of TFTs of that column. A circuit for driving the scan line is called a scan line driver circuit, and a circuit for driving the signal line is called a signal driver circuit. A circuit for driving the display unit including the scan line and signal line drivers is collectively called a peripheral circuit.
An active matrix liquid crystal display apparatus of the type using TFTs as switching elements for pixel electrodes, is more suitable for multi-pixel and provides clearer images, than a simple matrix liquid crystal display apparatus having crossed wiring lines on a pair of substrates. Recently, most of display units of personal computers, video cameras (view finders) and the like use active matrix liquid crystal display apparatuses.
A number of pixel electrodes and thin film transistors are formed on a transparent glass substrate to fabricate an active matrix liquid crystal display apparatus. A silicon crystallization process accompanied with high temperature annealing is difficult to be applied to a transparent glass substrate. As TFTs used by a liquid crystal display apparatus, amorphous silicon TFTs able to be manufactured at a low temperature have been used.
However, the mobility of electrons and holes in amorphous silicon is as small as about 1 cm2/Vs. An amorphous silicon TFT using amorphous silicon as a channel layer is difficult to be switched at high speed. To solve this problem, the following structures have been proposed. Namely, a chip of a peripheral circuit formed on a single crystal silicon substrate is mounted on the glass substrate of the liquid crystal display apparatus, or a flexible circuit board with a peripheral circuit chip is adhered to the glass substrate.
Techniques of polycrystallizing amorphous silicon through laser annealing have also been adopted.
If the pixel electrodes formed on a TFT substrate of an active matrix type liquid crystal display apparatus are made of reflection electrodes, a reflection type liquid crystal display apparatus can be formed.
This reflection type liquid crystal display apparatus does not require back light as in the case of a transmission type liquid crystal display apparatus. As compared to a transparent liquid crystal display apparatus, it can be made less in power consumption, thinner, more compact, and lighter in weight.
A reflection type liquid crystal display apparatus is easy to be applied to a projector panel. A projector panel using the reflection type liquid crystal display apparatus can be made more compact and precise and can use more inexpensive optical systems than a transmission type liquid crystal display panel. In addition, a projector panel using a reflection type liquid crystal display apparatus can be made to have a ultra high luminance. It also has a high reliability because of less optical degradation and ease of panel cooling.
A conventional reflection type liquid crystal display apparatus is, however, associated with the following problems.
1) Problem of Coupling
Electrical coupling occurs among reflection electrodes, signal bus lines and TFTs. The electrical characteristics and optical quality of a liquid crystal display apparatus may be degraded by flicker capacitance and crosstalk capacitance.
(2) Problem of Crosstalk by Photocurrent
In a reflection type liquid crystal display apparatus, light passing through an opposing substrate (second substrate) may become incident upon the first substrate through a gap between reflection electrodes. If this light enters a pixel TFT of the display unit, display degradation such as crosstalk may be caused by photocurrent generated by TFT.
It is desired to monolithically fabricate a display unit and a peripheral circuit on the same substrate in order to reduce a manufacture cost of a liquid crystal display apparatus and raise a manufacture efficiency.
It is an object of the present invention to provide a liquid crystal display apparatus having a peripheral circuit integrated with a display unit and providing a high speed operation.
It is another object of the invention to provide a reflection type liquid crystal display apparatus with fine pixels formed in a display unit, and a display panel using such a reflection type liquid crystal display apparatus.
According to one aspect of the present invention, there is provided a liquid crystal display apparatus comprising: a first substrate; a display section formed on the first substrate and including a plurality of pixels disposed in a matrix pattern, a plurality of scan lines extending in a row direction and a plurality of signal lines extending in a column direction, wherein one pixel is connected at each cross point between the scan and signal lines and each pixel includes a semiconductor active element and a pixel electrode; a first peripheral circuit disposed at opposite end portions of the first substrate in the row direction and including a scan line driver circuit including semiconductor active elements for driving the scan lines; a second peripheral circuit disposed at opposite end portions of the first substrate in the column direction and including a signal line driver circuit including semiconductor active elements for driving the signal lines; a transparent second substrate disposed opposing the first substrate; a liquid crystal layer sandwiched between the first and second substrates; and an insulating black color shading film formed on an inner surface of the second substrate and covering at least a partial area of the second peripheral circuit.
According to another aspect of the present invention, there is provided a reflection type liquid crystal display apparatus comprising: a first substrate including a display section with a plurality of pixels disposed in a matrix pattern; a second substrate disposed opposing the first substrate and formed with a first common electrode; and a liquid crystal layer sandwiched between the first and second substrates, wherein the display section of the first substrate comprises: a plurality of semiconductor active elements disposed in a matrix pattern, each having a source, a drain and a gate; an interlayer insulating film deposited covering the semiconductor active elements; a plurality of scan lines formed in the interlayer insulating film each for connecting the gate of the semiconductor active element dispose in a row direction; a plurality of signal lines formed in the interlayer insulating film each for connecting the source of the semiconductor active element disposed in a column direction; a second common electrode formed in the interlayer insulating film at a level higher than the scan and signal lines, covering a plurality of pixels, electrically connected to the first common electrode, and having an opening above the drain of each semiconductor active element; and a plurality of pixel electrodes formed on the interlayer insulating film, each being connected to the drain of a corresponding one of the semiconductor active element by penetrating through a contact hole formed in the interlayer insulating film in an area corresponding to the opening, the pixel electrode being separated for each pixel and opposing the first common electrode via the liquid crystal layer.
As above, in a peripheral circuit integrated liquid crystal display apparatus, an insulating black color shading film covering at least a partial area of the peripheral circuit thin film transistors constituting the signal line driver circuit is formed. It is therefore possible to prevent malfunction of TFTs to be caused by incidence light and also prevent large parasitic capacitance to maintain a high operation performance of the peripheral circuit.
By using the reflection type liquid crystal display apparatus of the invention, high integration and high performance of the reflection type liquid crystal display apparatus can be realized.